ZHCSHR0B September 2017 – September 2019 BQ25910
PRODUCTION DATA.
The three-level converter is a combination of a switched capacitor and a switched inductor circuit. Assuming the flying capacitor, CFLY, remains balanced at VIN/2, the VSW node can be presented with three different voltages: VIN, VIN/2, and GND. The gate driving scheme is similar to a two-phase buck converter. The outer FETs (QHSA and QLSA) are driven with a complimentary signal with duty cycle D = VOUT/VIN. The inner FETs (QHSB and QLSB) are driven with a second complimentary signal of equal duty cycle, but phase shifted by 180°. By employing this driving scheme, there is a smooth transition around 50% duty ratio, where the VSW node moves from presenting GND and VIN/2 to presenting VIN and VIN/2.
The three-level can achieve higher efficiency which cannot be easily obtained using traditional buck converter. The high efficiency is due to reduced inductor ripple (volt-seconds), reduced switching loss, and use of a compact inductor with lower DCR. The device integrates low RDSON FETs to optimize conduction loss. It also integrates control circuit to monitor CFLY stability and pre-conditioning.